Field of the Invention
The present invention relates to an aluminum wired layer for interconnecting devices on a semiconductor device and a method of manufacturing an aluminum wired layer, and more particularly to an aluminum wired layer for interconnecting devices on a semiconductor device, with the aluminum wired layer being formed with an Al-Ti compound metal layer on the periphery of the aluminum wired layer, for example, top, bottom and side walls, and to a method of manufacturing such aluminum wired layer.
In general, in manufacturing a semiconductor device, the material of the aluminum wired layer interconnecting the devices for certain purposes formed inside the semiconductor device is a material which has excellent electric conductivity and which easily accepts the depositing process and the mask patterning process as final processes. Aluminum is the most widely used material.
The advantages of aluminum, in addition to the above description, are its good adherence to the top of the oxide film during the wiring process and its ability to bond with gold wire or aluminum wire. Further, aluminum is inexpensive.
On the other hand, aluminum has various problems. First, silicon diffuses from the silicon substrate into the aluminum wired layer at the junction positioned between the aluminum wired layer and the silicon substrate. This results in the formation of an undesirable pit in a portion of the junction which destroys the junction. This occurs when manufacturing an aluminum wired layer on a silicon substrate when heat (400-500 degree Celsius) is used to enhance the junction between the aluminum wired layer and the silicon substrate. This also occurs in other heat treatment processes, such as the depositing process (350-450 degree Celsius) where an insulation layer is deposited on the aluminum wired layer after the aluminum wired layer is formed on the silicon substrate. In view of the above, silicon is added, approximately 1% by weight, to the aluminum which will form the aluminum wired layer. The silicon is added to prevent the silicon of the substrate from diffusing into the aluminum wired layer during heat treatment of the aluminum wired layer. The metal barrier layer, such as TiW (Titanium - Tungsten) layer (10% Titanium/90% Tungsten) or TiN (Titanium - Nitride) layer can also be used to prevent the silicon of the substrate from diffusing into the aluminum wired layer during heat treatment of the aluminum wired layer deposited thereon.
Second, in the heat treatment process described above, a hillock of aluminum projecting from the surface of the aluminum wired layer occurs due to the difference in the thermal expansion coefficient between the aluminum wired layer and the substrate below the layer. Thus, when depositing a protecting film on the entire structure after the process of forming the aluminum wired layer for an internal connection line and performing the process of packaging the device, if the lithographic etching process utilizing a photoresist is performed for removing only a portion of the protecting film, such as for example, the bonding pad portion at which an aluminum wired layer for external connecting line is connected to the aluminum wired layer for internal connection line, the hillock causes a problem that the protecting film cannot protect against because the photoresist cannot cover completely the surface of the aluminum wired layer except for a portion of the bonding pad portion such that the protecting layer at the hillock is undesirably etched away. Furthermore, in the case of forming a multi-layered metal wired layer, a pin hole is produced at the insulating layer due to the hillock so that the lower aluminum wired layer and the upper aluminum wired layer are electrically connected to each other at an undesirable position rendering the device inoperable.
Third, when the device operates, the flow of electric current in the aluminum wired layer results in an electromigration phenomenon in which the atoms of the aluminum move so that the aluminum wired layer becomes disconnected.
One of the methods of the prior art to solve hillock formatting on the surface of the aluminum wired layer and the problem of the electromigration is to deposit an aluminum layer and a titanium layer in sequence, as shown in FIG. 1. A plurality of the aluminum wired layers is then formed by removing certain portions of the aluminum and the titanium layers by the mask patterning process. An Al-Ti compound metal layer is formed on the top of the aluminum wired layer by heat treatment. The Al-Ti compound metal layer restrains the occurrence of hillock formation and reduces the electromigration phenomenon. In the prior art process the Al-Ti compound metal layer is obtained by heat treatment of the aluminum wired layer and the titanium layer at the temperature of about 350-450 degree Celsius. It is noted that if the silicon is added in the order of less that 2% by weight in the aluminum, the Al-Ti compound metal layer is composed of the Al.sub.3 Ti.
However, with the prior art method, while the hillock on the top of the aluminum wired layer can be restrained, the hillock projected from the side wall of the aluminum wired layer cannot be restrained. However, the spacing between the adjacent aluminum wired layers is small making adjacent layers undesirably connected to each other where the hillock occurs at the side wall. This results in a failure of the device.
Therefore, an object of the present invention is to provide an aluminum wired layer for connecting device to device in a semiconductor device constructed in such a way that the Al-Ti compound metal layer is formed over the entire exposed surface of the top, bottom and side walls of the aluminum wired layer.
A further object of the present invention is to provide a method for forming a protected aluminum wired layer.
A further object of the present invention is to provide an aluminum wired layer for connecting device to device which restrains the occurrence of hillock formation not only on the top but also on the side walls of the aluminum wired layer.
A further object of the present invention is to provide an aluminum wired layer for connecting device to device which prevents the occurrence of the destruction of the junction between the aluminum wired layer and the silicon substrate, and which prevents the electromigration phenomenon in the aluminum wired layer.
The preceeding objects should be construed as merely presenting a few of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to both the summary of the invention and the detailed description, below, which describe the preferred embodiment in addition to the scope of the invention defined by the claims considered in conjunction with the accompanying drawings.